The present invention concerns a vehicle headlamp having a control for selectively rendering portions of the headlamp light transmissive under vehicle operator control.
All motor vehicles include a control for switching between high beam and low beam operation of the motor vehicle headlamps. This control may be implemented by a floor mounted switch but most typically in more recent designed motor vehicles is implemented with a stalk on the vehicle steering column that is easily actuated by a motor vehicle operator.
When the high beam option is selected, the vehicle headlamps are focused in a direction that illuminates further in advance of the vehicle to improve a motorist""s ability to see details in his or her line of sight. When an oncoming vehicle approaches, the motorist can switch to low beam operation to avoid temporarily blinding the oncoming driver. Fog lamps are occasionally installed on vehicles to direct a lamp output downward in a direction closer to the vehicle to enable the motorist to more clearly see during rain and foggy conditions.
Vehicle head lamps most typically contain two separate light bulbs that can be independently activated. When one of the bulbs is activated, a low beam lamp output is produced and when a second bulb of the two bulbs is activated a high beam lamp output is provided. In the 1980""s when headlamps having halogen light bulbs were first built, the government enacted photometric tests. These tests dictated that light of a high enough intensity to cause spot blindness in other motorists did not reach certain regions in a space in front of a motor vehicle headlamp. Spot blindness was only a problem for halogen lights since these lights produce a much more intense output when compared with non-halogen lamps.
U.S. Pat. No. 5,517,389 to Meyers concerns an electrochromic lamp assembly including a reflector having two or more reflective surfaces. A light source and an electrochromic means is positioned between the light source and at least one reflective surface. Each reflective surface directs light in a different direction. The electrochromic means is capable of blocking light from exiting the lamp assembly from at least one direction.
The present invention concerns a headlamp assembly for use with a motor vehicle. The headlamp assembly includes regions on a light transmitting portion of an assembly housing that can be selectively controlled to change from opaque to highly transmissive. The headlamp assembly can operate as a fog lamp, can provide a low beam output lamp, can provide a high beam output lamp and can provide various combinations of these lamp operations.
One exemplary embodiment of a headlamp assembly constructed in accordance with the invention includes a headlamp bulb for emitting light from the headlamp assembly that is supported by a bulb housing having a light transmissive portion for transmitting light from the headlamp bulb to an illumination zone. At least a portion of the housing is coated with a coating material which covers a selected region of the light transmissive portion of the housing. By electrically energizing the coating material, its light transmissive properties are controlled, thereby controlling an amount of light transmitted from the bulb to the illumination zone. A drive circuit is electrically coupled to the coating material.
Practice of the exemplary embodiment of the invention gives a motorist direct control of intensity and zones of illumination. The motorist can adjust the illumination intensity and zone for specific traveling conditions, i.e. weather, terrain, time of day etc. This creates a safer environment to operate the motor vehicle.
Practice of the exemplary embodiment of the invention is achieved with one, high intensity bulb supported by a headlamp assembly having a reflective region for directing light through the light transmissive portion of the assembly. This structure produces high beam, low beam and fog lamp outputs without resort to multiple bulbs and bulb housings.
The exemplary embodiment of the invention includes multiple regions that are defined by the coating material. These photometric patches eliminate a need for a bulb shield. Current commercially available bulb shields are made specifically for a high beam, low beam or fog lamp bulb housing. Alternatively, the bulb shield must be mechanically repositioned inside a bulb housing. Either of these two techniques is more complex and costly than a headlamp assembly built in accordance with the present invention.
A preferred coating material is a PDLC material (polymer dispersed liquid crystal) which scatters light rather than absorbing the light to block its transmission. This characteristic greatly reduces heat build up associated with masking a halogen lamp, whose high intensity light output causes a rapid build up of heat in any material which absorbs that light.
These and other objects, advantages and features of the invention will become better understood from a detailed description of an exemplary embodiment of the invention which is described in conjunction with the accompanying drawings.